The functionality of the human vomeronasal organ (VNO): evidence for steroid receptors

The human vomeronasal organ (VNO) is an anatomical entity which is generally considered to be vestigial or non-functional. Nevertheless, a steroidal vomeropherin applied to the human VNO, results in changes of autonomic function, pulsatile release of luteinizing and follicle-stimulating hormones, autonomic and electroencepholographic activity. The vomeropherin pregna-4,20-diene-3,6-dione (PDD) was delivered as pulses in an air stream directed into the lumen of the VNO or to the surface of the olfactory epithelium and respiratory epithelium of the nasal septum. Single stimuli at a concentration of 10(-10) to 10(-8) M produced dose-dependent changes of the electrovomerogram. No significant effects were observed when the same applicator delivered identical stimuli to the nasal respiratory epithelium or to the olfactory epithelium. Administration of the vomeropherin to male subjects changed gonadotropin pulsatility. In males, PDD (5 x 10(9) M) decreased luteinizing hormone (LH) pulsatility which resulted in a statistically significant reduction of plasma LH levels (P < 0.009) and follicle-stimulating hormone (FSH) pulsatility (P < 0.021), but it produced no significant effects in female subjects. Prolactin (PRL) was not significantly affected by this vomeropherin in either male or female subjects. These data demonstrate, for the first time, the existence of a functional vomeronasal-pituitary pathway in adult humans. In addition to the effect on gonadotropin pulsatility, the vomeropherin also produces concurrent reflex autonomic effects after VNO stimulation. These included decreased respiratory frequency, increased cardiac frequency, and event-related changes of electrodermal activity and EEG pattern. Therefore, this investigation also provides evidence for functional connections between the VNO and a variety of hypothalamic areas in adult humans.